This invention relates to a rolling mill for rolling a strip material or a bar material, which passes through upper and lower work rolls, to a predetermined thickness. More particularly, the invention relates to a rolling mill preferred for use in hot rolling.
FIG. 15 schematically shows a conventional four high cross rolling mill, and FIG. 16 schematically shows an essential part for illustrating a roll replacement operation in a cross rolling mill.
As shown in FIG. 15, upper and roller work roll chocks 002 and 003 as a pair are supported inside a housing 001. Shaft portions of upper and lower work rolls 004 and 005 as a pair are rotatably supported by the upper and lower work roll chocks 002 and 003, respectively, and the upper work roll 004 and the lower work roll 005 are opposed to each other. Upper and lower backup roll chocks 006 and 007 as a pair are supported above and below the upper and lower work roll chocks 002 and 003. Shaft portions of upper and lower backup rolls 008 and 009 as a pair are rotatably supported by the upper and lower backup roll chocks 006 and 007, respectively. The upper backup roll 008 and the upper work roll 004 are opposed to each other, while the lower backup roll 009 and the lower work roll 005 are opposed to each other. A screw down device 010 for imposing a rolling load on the upper work roll 004 via the upper backup roll chock 006 and the upper backup roll 008 is provided in an upper portion of the housing 001.
Upper crossheads 011 and 012 for horizontally supporting the upper backup roll chock 006 and the upper work roll chock 002 are provided in the upper portion of the housing 001 and positioned on an entry side and a delivery side of the housing 001. The upper crossheads 011, 012 are horizontally movable by screw mechanisms 013, 014. Lower crossheads 015 and 016 for horizontally supporting the lower backup roll chock 007 and the lower work roll chock 003 are provided in a lower portion of the housing 001 and positioned on the entry side and the delivery side of the housing 001. The lower crossheads 015, 016 are horizontally movable by screw mechanisms 017, 018.
Thus, when rolling is performed, a strip S is fed from the entry side of the housing 001, and passed between the upper work roll 004 and the lower work roll 005 given a predetermined load by the screw down device 010, whereby the strip S is rolled. The rolled strip S is delivered from the delivery side and supplied to a subsequent step.
The screw mechanisms 013, 014, 017, 018 are actuated before or during rolling, whereby the upper chocks 002, 006 and the lower chocks 003, 007 are moved in different directions via the crossheads 011, 012, 015, 016. As a result, the upper work roll 004 and the upper backup roll 008, and the lower work roll 005 and the lower backup roll 009 are turned in opposite directions about a roll center so that their rotation axes may cross each other and the angle of their crossed axes may be set at a required angle. By so doing, the strip crown is controlled.
For roll replacement, moreover, the screw mechanisms 013, 014, 017, 018 are actuated to separate the crossheads 011, 012, 015, 016 from the chocks 002, 003, 006, 007 and form gaps g between the roll chocks 002, 003, 006, 007 and the crossheads 011, 012, 015, 016, as shown in FIG. 16. Thus, the upper and lower work rolls 004 and 005 and the upper and lower backup rolls 008 and 009 can be withdrawn from a work side by a predetermined device without interference by the crossheads 011, 012, 015, 016, and can be replaced with new ones.
In all rolling mills including the foregoing four high cross rolling mill, hysteresis during vertical control of the work rolls 004, 005 and backup rolls 008, 009 in the housing 001 needs to be minimized in a rolling condition under a screw down force F to control the thickness of a rolled plate highly accurately. For this purpose, gaps G are formed between the work roll chocks 002, 003 and backup roll chocks 006, 007 and the crossheads 011, 012, 015, 016 or housing 001.
Thus, as shown in FIG. 17, even when deformation in an inward narrowing amount of xcex4 is caused to the housing 001 under the screw down load F during rolling, gaps of about 0.2 mm to 1.0 mm are present between the roll chocks 002, 003, 006, 007 and the housing 001 or crossheads 011, 012, 015, 016, so that the horizontal dynamic stiffness of the rolling mill may be low. If rolling is performed with a high rolling force and a high percentage reduction in the thickness of the strip while the horizontal dynamic stiffness of the rolling mill is low, great vibrations probably attributed to, for example, friction between the strip S being rolled and the work rolls 004, 005 (hereinafter referred to as mill vibrations) occur in the housing 001 or the work rolls 004, 005, thereby impeding high efficiency rolling.
As means of preventing vibrations in a rolling mill, Japanese Unexamined Patent Publication No. 1997-174122 discloses a rolling mill provided with a damper comprising a piston, a cylinder and an orifice between an upper work roll and a lower work roll. However, the vibration preventing device of the rolling mill disclosed in this publication is applied to cold rolling, and its application to hot rolling is difficult. That is, in cold rolling, a strip maintained in a room temperature condition is engaged at a low speed between upper and lower work rolls, and continuously rolled. In hot rolling, on the other hand, a strip heated in a high temperature state is engaged at a high speed between upper and roller work rolls, and rolled for each coil of a predetermined length. Thus, hot rolling causes a higher impact force at the time of engagement of the strip with the upper and lower work rolls, and faces impact more frequently, than cold rolling. Furthermore, hot rolling has a greater rolling amount of the strip (a higher rolling force on the strip) than cold rolling, so that the frictional force acting between the work roll and the strip is also higher. This is another factor which makes the impact force greater during engagement. As noted here, hot rolling generates a higher impact force during strip engagement than cold rolling. Hence, the aforementioned vibration preventing device of the rolling mill, which is applied to cold rolling, cannot fully prevent roll vibrations during rolling.
The present invention has been accomplished to solve these problems, and its object is to provide a rolling mill which eliminates gaps between roll chocks and a housing during rolling to increase horizontal dynamic stiffness, thereby suppressing mill vibrations and permitting high efficiency rolling.
A rolling mill of the present invention for attaining the above-mentioned object comprises a housing, upper and lower work roll chocks as a pair supported by the housing, upper and lower work rolls as a pair opposed to each other and having shafts rotatably supported by the upper and lower work roll chocks, screw down means provided in an upper portion of the housing and adapted to apply a predetermined pressure to the upper work roll, first upper and lower support means as a pair provided on one side in a transport direction of a strip material in the housing and adapted to support the upper and lower work roll chocks, and second upper and lower support means as a pair provided on the other side in the transport direction of the strip material in the housing and adapted to support the upper and lower work roll chocks, one of the first support means and the second support means is mechanical thrust means, while the other of the first support means and the second support means is hydraulic thrust means, and contraction portions are provided in hydraulic supply and discharge pipes of the hydraulic thrust means.
Thus, the first thrust means and the second thrust means are actuated during rolling to eliminate gaps between the roll chocks and the housing and increase the horizontal dynamic stiffness, thereby suppressing mill vibrations and permitting high efficiency rolling.
In the rolling mill of the present invention, the rolling mill may be a cross rolling mill with the upper and lower work rolls slightly crossing each other, the first support means may be entry-side thrust means provided on an entry side of the housing and capable of thrusting the upper and lower work roll chocks in the transport direction of the strip material, and the second support means may be delivery-side thrust means provided on a delivery side of the housing and capable of thrusting the upper and lower work roll chocks in the transport direction of the strip material. By so doing, high efficiency rolling can be performed in the cross rolling mill with mill vibrations being suppressed.
In the rolling mill of the present invention, the mechanical thrust means may be screw mechanisms. By so doing, positioning of the rolls during rolling can be performed with high accuracy.
In the rolling mill of the present invention, the mechanical thrust means may be wedge mechanisms. By so doing, positioning of the rolls during rolling can be performed highly accurately without rattling. Furthermore, the structure can be simplified to decrease the manufacturing cost.
In the rolling mill of the present invention, there may be provided upper and lower backup roll chocks as a pair supported by the housing, and upper and lower backup rolls as a pair opposed to each other and having shafts rotatably supported by the upper and lower backup roll chocks, one of upper and lower entry-side thrust means and delivery-side thrust means as a pair capable of thrusting the upper and lower backup roll chocks in a horizontal direction may be mechanical thrust means, while the other of the entry-side thrust means and delivery-side thrust means may be hydraulic thrust means, and contraction portions may be provided in hydraulic supply and discharge pipes of the hydraulic thrust means. By so doing, at the positions of the backup rolls as well as at the positions of the upper and lower work rolls, gaps between the roll chocks and the crossheads or the housing during rolling are eliminated to increase the horizontal dynamic stiffness, thereby suppressing mill vibrations and permitting high efficiency rolling.
In the rolling mill of the present invention, the diameters of the contraction portions may be variable. Thus, the workability can be increased, and vibrations can be suppressed efficiently, by adjusting the diameters of the contraction portions to appropriate values during rolling, or at the time of setting a roll cross angle, or in accordance with the magnitude of vibrations.
In the rolling mill of the present invention, the diameters of the contraction portions may be maximized at the time of setting a cross angle between the upper and lower work rolls, and the diameters of the contraction portions during rolling by the upper and lower work rolls may be set at appropriate predetermined values for each of the rolling conditions. By so doing, the diameters of the contraction portions are maximized at the time of setting the roll cross angle, so that the work rolls can be moved smoothly. During rolling, the diameters of the contraction portions are adjusted to appropriate values, whereby vibrations can be suppressed reliably.
In the rolling mill of the present invention, the contraction portions may be electromagnetic valves. By the changing operation of the electromagnetic valves, maximization and minimization of the contraction portions can be carried out smoothly to increase workability.
In the rolling mill of the present invention, enlarged portions may be provided in the hydraulic supply and discharge pipes. By so doing, a pressure wave generated in the hydraulic supply and discharge pipe by mill vibrations, etc. is suppressed at the enlarged portion, so that occurrence of a resonance phenomenon can be prevented.
In the rolling mill of the present invention, the rolling mill may be an offset rolling mill in which upper and lower backup rolls as a pair in contact with the upper and lower work rolls, respectively, may be supported by the housing via backup roll chocks, and the upper and lower backup rolls may be slightly displaced relative to the upper and lower work rolls rearward in the transport direction of the strip material, the first support means may be hydraulic thrust means provided on one of an entry side and a delivery side of the housing, being capable of thrusting the upper and lower work roll chocks in the transport direction of the strip material, and having the contraction portions, and the second support means may be housing liner portions provided on the other of the entry side and the delivery side of the housing.
By so doing, high efficiency rolling can be performed in the offset rolling mill, with mill vibrations being suppressed.
In the rolling mill of the present invention, the rolling mill may be a shift rolling mill for shifting the upper and lower work rolls as a pair in a roll axis direction, the first support means may be hydraulic thrust means provided on one of an entry side and a delivery side of the housing, being capable of thrusting the upper and lower work roll chocks in the transport direction of the strip material, and having the contraction portions, and the second support means may be housing liner portions provided on the other of the entry side and the delivery side of the housing. By so doing, high efficiency rolling can be performed in the shift rolling mill, with mill vibrations being suppressed.